1. Field of the Invention
The invention cavity resonator multi-cavity klystron, and more particularly to a multi-cavity klystron having a cavity resonator operated by an induction or L-tuning process.
2. Description of the Related Art
As known to those skilled in the art, a multi-cavity klystron comprises an electron gun transmitting a beam of electrons, a collector which captures the beams of electrons, and a high frequency circuit which interacts with the beam of electrons. The high frequency circuit has a plurality of cavity resonators arranged in series. Each of the cavity resonators in the high frequency circuit is constructed so that a resonance frequency thereof can be varied to vary an amplitude versus frequency characteristic and an available channel of the klystron. As is well known, methods for varying a resonance frequency include C-tuning process wherein a capacity of the resonance cavity is varied, an L-tuning process wherein then induction is varied, and combinations of these two processes. With respect to the electrical characteristic, the L-tuning process is most preferable because a high impedance for the resonance cavity can be obtained.
Hereinbelow will be explained the principle underlying the L-tuning process, with reference to FIGS. 1A and 1B.
FIGS. 1A and 1B are transverse and longitudinal cross-sectional views of a cavity resonator of a conventional multi-cavity klystron. As illustrated, a cavity resonator has a cavity envelope 1 and drift tubes 2 both of which define a resonance cavity 3. In the resonance cavity 3 is inserted a movable tuning element 6 comprising a column-shaped spring carrier 4 having opposite end surfaces 4b and 4c in parallel to each other (see FIG. 1A). The spring carrier 4 is formed at an outer surface thereof with a spiral, thin groove 4a for accommodating a spring therein (see FIG. 1A). In the spiral groove 4a is inserted a resilient metal wire 11. Conventionally, a tungsten wire often has been used as the metal wire 11. As illustrated in FIG. 1B, parts of the metal wire 11 which protrude from the spring carrier 4 toward top and bottom of the cavity envelope 1 are in contact with upper and lower internal surfaces 7a and 7b of the resonance cavity 3. The spring carrier 4 is interposed between parallel plates 8a and 8b of a tuning element support 8, and is secured to the support by means of a screw 8c, as illustrated in FIG. 1. The support 8 is connected to a connecting rod 9, a larger diameter end 9a of which is located outside the resonance cavity 3. Around the connecting rod 9 is provided a bellows 10 between the end 9a of the connecting rod 9 and the cavity envelope 1.
In operation of the above mentioned cavity resonator, the connecting rod 9 is axially moved to thereby slide the movable tuning element 6 on the upper and lower internal surfaces 7a and 7b of the resonance cavity 3. Thus, a volume of the resonance cavity 3 or an inductance can be varied to thereby vary a resonance frequency of the cavity envelope 1.
Next, it will be explained how the movable tuning element 6 is centered transversely with reference to FIGS. 2A and 2B.
FIGS. 2A and 2B are transverse and longitudinal cross-sectional views illustrating a conventional method disclosed in Japanese Unexamined Patent Public Disclosure No. 2-18254 for transversely centering a movable tuning element. As illustrated, the spring carrier 4 is formed at the end surfaces 4b and 4c (see FIG. 2A) thereof with recesses 4d for receiving springs 12. The springs 12 received in the recesses 4d project from the end surfaces 4b and 4c of the spring carrier 4 and keep in contact with the upper and lower internal surfaces 7a and 7b (see FIG. 2B) of the cavity envelope 1. The tuning element 6 is hereby transversely centered in the resonator cavity 3.
FIG. 3 is a longitudinal cross-sectional view illustrating a conventional mechanism disclosed in Japanese Unexamined Patent Public Disclosure No. 58-88765 for tuning a multi-cavity klystron. As illustrated, a multi-cavity klystron is tuned by rotating a tuning screw 17 located outside the cavity envelope 1, which is kept in vacuum, to thereby displace an induction plate 14. The centering of the induction plate 14 is accomplished by coupling a tuning shaft 13 into the tuning element support 8 and also by coupling a tuning stopper 16 into the tuning element support 8.
However, when the aforementioned conventional methods are applied to a multi-cavity klystron having a high frequency greater than 14 GHZ band, for transversely centering the tuning element 6 or the induction plate 14, problems arise, as follows.
A. In the method illustrated in FIGS. 2A and 2B, as a higher frequency is used, a size of the cavity resonator has to be reduced and hence the spring carrier 4 has to be reduced in size as well. As a result, it is impossible to provide a space for attaching the spring 12 to the spring carrier 4.
B. In the method illustrated in FIG. 3, since the centering of the induction plate 14 is accomplished by the tuning screw 17, which is located outside the cavity envelope 1, it is impossible to avoid the generation of play between the tuning screw 17 and the induction plate 14 even if the tuning shaft 13 and the tuning stopper 16 are precisely coupled into the tuning element support 8. As a result, the induction plate 14 is not centered, and accordingly the induction plate 14 often unnecessarily contacts with the left and right internal surfaces of the cavity envelope 1.